Countercurrent catalytic contact of a reactant stream in a multiple-stage process and the apparatus therefor

ABSTRACT

A unitary, multiple-stage reaction system for countercurrently contacting a fluid reactant stream with catalyst particles movable through the system via gravity-flow. The reaction zones, or stages, are vertically stacked in a single chamber wherein catalyst particles flow from one annular-form bed to the next lower annular-form bed. A first portion of the hydrocarbonaceous charge stock flows downwardly into the lowermost reaction zone, laterally (outward to inward flow) through the annular-form catalyst bed into a center reactant conduit, is admixed with the second portion of the charge stock, flows upwardly through the reactant conduit into the next upper zone and laterally (inward to outward flow) through the annular-form catalyst bed. A preferred embodiment involves three reaction zones within the reaction chamber, with heat-exchange provisions between the middle and upper zones.

United States Patent n91 Forbes et al.

[ COUNTERCURRENT CATALYTIC CONTACT OF A REACTANT STREAM IN AMULTIPLE-STAGE PROCESS AND THE APPARATUS THEREFOR [75] inventors: JamesT. Forbes. Arlington Heights:

James E. Gantt. Elmwood Park. both of ill.

[73] Assignee: Universal Oil Products Company. Des Plaines. ill.

[22] Filed: Aug. 27, 1974 [21] Appl. No.: 501.001

Related US. Application Data [62] Division of Ser. No. 399.775. Sept.20. i973.

[52] US. Cl. 48/214: 23/288 6; 23/288 R; 48/l97 R; 208/169. 423/659 [5|]Int. Cl. ClOG 11/28 [58] Field oi Search 48/2l4. 213. 208; 23/288 G:208/]69. I65. l7l; 252/373: 423/659 [56] References Cited UNITED STATESPATENTS 2.512.562 6/l950 Cummings 23/288 1.837.822 9/i974 Ward 48/2l4 i1 Nov. 11. 1975 Primary Emminer-Robert L. Lindsay. Jr. AssislamEruminer-George C. Yeung Attorney. Agent. or Firm-James R. Hoatson. Jr.;Robert W. Erickson; William H. Page. ii

[57] ABSTRACT A unitary. multiple-stage reaction system forcountercurrently contacting a fluid reactant stream with cata lystparticles movable through the system via gravityflow. The reactionzones. or stages. are vertically stacked in a single chamber whereincatalyst particles flow from one annular-fomi bed to the next lowerannular-form bed. A first portion of the hydrocarbonaceous charge stockflows downwardly into the lowermost reaction zone. laterally (outward toinward flow) through the annular-form catalyst bed into a centerreactant conduit. is admixed with the second portion of the chargestock. flows upwardly through the reactant conduit into the next upperzone and laterally (inward to outward flow) through the annularformcatalyst bed. A preferred embodiment involves three reaction zoneswithin the reaction chamber. with heat-exchange provisions between themiddle and upper zones.

4 Claim 2 Drawing Figures U.S. Patent Nov. 11, 1975 FigureCOUNTERCURRENT CATALYTIC CONTACT OF A REACTANT STREAM IN AMULTIPLE-STAGE PROCESS AND THE APPARATUS THEREFOR Related ApplicationApplicability of Invention The present invention is directed toward animproved means and method for effecting the multiplestage,countercurrent catalytic "contact of a reactant stream and, moreparticularly, to a process and system stream is caused to flow laterallyand radially through the catalyst, is that described in U.S. Pat. No.2,683,654 (Cl. 23-388). The type of reactor the "stacked" configurationas shown in U.S. Pat. No 3,647,680 (Cl. 208-65); this is a two-stagesystem with an integrated regeneration facility which receives thecatalyst withdrawn from the bottom reaction chamber. The latter twotechniques make use of a downwardlymoving bed of catalyst particlesthrough which the reactant stream flows laterally and radially.

It must be noted that none of these recognize countercurrent hydrocarbonprocessing, and certainly not in combination with a reaction system inwhich the catalyst particles are movable via gravity-flow. it isacknowledged that some processes have been considered for countercurrentflow of the reactant stream; that is,

' flowing the feed stream upwardly through a fixed-bed wherein thecatalyst particles are movable via gravityflow. Applicable to-bothexothermic and endothermicv reaction systems, our invention alsoprovides for the introduction of a heat-exchange fluid stream intoan-intermediate mixing zone between two of thecatalytic stages orreaction zones.

Various types of multiple-stage reaction systems have experiencedwidespread utilization throughout the petroleum and petrochemicalindustries for effecting multitudinous reactions, and especiallyhydrocarbon conversion reactions. Such reactions are either principallyexothermic, or'endothermiqand include both hydrogen-producing andhydrogen-consuming reactions. Similarly, a wide spectrum of designs andarrangements have been proposed to effect the countercurrent con- .ofcatalyst particles. However, there is no awareness of combiningcountercurrent flow of the reactant stream with a downwardly-moving bedof catalyst particles.

As hereinbefore stated, the present inventive concept is directed towarda multiple-stage reaction system for countercurrently contacting a fluidreactant stream version of the charge stock and for, thepurpose of i Itroducing heating or cooling media into the reaction chamber atintermediate loci between the catalytic stages.

Multiple-stage reaction systems are generally-of twoentire system viagravity-flow. Although applicable to all the foregoing reactorconfigurations, processes and reactions, the multiple-stage reactionsystem herein described is rnost readily adaptable for use in effectingthose hydrocarbon conversion reactions wherein the rate and degree ofcatalyst deactivation increases in the direction of reactant streamflow.

OBJECTS AND EMBODIMENTS One object of our invention is to provide amultiplestage reaction system for countercurrently contacting a fluidreactant stream with-catalyst particles movable I through the system byway of gravity-flow. A corollary types: (1)side-by-sideconfiguration,with intermediate heating and/or coolingbetween zones, wherein the reactant stream or mixture "flow seriallyfrom zone-ito zone; and, (2) a stacked design wherein asingle reactionchamber contains the multiple contactstages, Such systems, as applied topetroleumrefining, have" been employed to'effect numeroushydrocarbon'conversion reactions including those which are' prevalent incatalytic reforming, fixed bed alkylationg ethylben zene dehydrogenationto producestyrene,,other 'dehydrogenation' processes, hydrorefining',isom'e'ri zation,

desulfurization, hydrocracking,hydrognationQtransalQ kylation, fsteamreformingfor 'substitute natural gas (SNG) productiomfetc. it willbeimmediately recog f objective resides in affording a reaction systemfor effecting the countercurrent, vapor-phase contact of a reactantfeed-stream with catalyst particles disposed as annular beds, and inwhich they are movable via gravity-flow.

.A more specific object is to afford a technique for effecting thosehydrocarbon conversion reactions in which the rate and degree ofcatalyst deactivation increases irt the direction of reactant streamflow.

Therefore, in one embodiment, our inventive concept encompasses aunitary,.- multiple-stage reaction system for countercurrentlycontacting a fluid reactant stream with catalyst particles movablethrough said systern via gravity-flow, which system comprises, incomnizedrthat someof theseprocesses are'exothermic e.g. hydrocrackingsome arefendotherrniii e. g; ethylbenzencdehydrogenation andsorneencompass both e.g. catalytic reforming. lt shouldbe'noted that,

these reactions are effected in;vapor-phase,' liquid '1.

phase of mixed-phase, depending principallyuponthe" charge stockcharacteristics and the ultimately desired product slate. I 7

Traditionally, hydrocarbon conversion processes have been effectedc'atalytieally in a fixed-bedsystem, either in downward flow, upwardflow, or in a lateral]? radial flow wherein the catalyst is disposeda's'an annular-form bed.. Many design and operating considerationsindicate the advantages-of annular-form, radial flow, particularly in avapor-phase operation. Illustrative of a reaction system, wherein thereactant-feed vscreensforming; (i) an annular-form catalyst-holdingsection therebetween, (ii) an annular-form void volume between the outerscreen and the interior wall of said chamber, and, (iii) acenterreactant conduit; (c)

-in the lowermost of said reaction zones, (i) a first ".lower,imperforate transverse partition connected to "nected to said inner andouter catalyst-retaining screens. and terminating at both the inner andouter screens;"(d) at least one other of said reaction zones,

vertically-disposed above said lowermost reaction zone, having (i) asecond lower, imperforate transverse partition. connected to said innerand outer retaining screens, and to the interior wall of said chamber,terminating at said inner retaining screen, and, (ii) a second upper,imperforate transverse partition connected to said inner and outerretaining screens, and terminating at said outer screen; (e)catalyst-transfer conduits connecting a catalyst-holding section withthe next succeeding lower catalyst holding section, andcatalystwithdrawal conduits extending downwardly through a lowerextremity of said chamber, whereby catalyst particles flow via gravityfrom one catalyst-holding section to a lower catalyst-holding section.and out of said chamber; (f) a first fluid'reactant inlet port in saidlowermost reactionzone at a locus between said first upper and saidsecond lower. imperforate transverse partitions; (g) a second fluidreactant inlet port in the bottom of said reaction'chamber, in opencommunication with said center reactant conduit; (h) a reaction productoutlet port in the upper end or, said chamber, inopen communication withthe uppermostannular-form. voidvolume; and*(i) -a' catalyst inlet portinthe upper, end of said chamber, in open communication, via cata--lyst-transfer conduits, with the uppermost catalystholding section; saidreaction system beingfurther characterized in that" said innercatalyst-retaining screen is'imperforate along that portion of itslength extending from said first upper, imperforate transverse partitionto said second lower imperforate transverse partition. In anotherembodiment, the reaction cham-' ber contains three reaction zones, thethird, uppermost one of which has disposed therein inner and outertubular-form, catalyst-retaining screens forming (i) an annular-formcatalyst-holding section therebetwecn, (ii) an annularform void volumebetween the outer screen and the interior wall of said chamber, and(iii)'a center reactant conduit. in 'still another embodiment, the threereaction zone system is further characterized in that the innercatalyst-retaining,screen is continuous through the lower two reactionzones, and terminates at its upper end at said second upper,imperforatetransverse partition. l a

The multiple-stage reaction system is advantageously utilized in aprocess for effecting the countercurrent contact and conversion of areactant stream with cata- 4 ing the resulting convened reactant streamfrom an upper portion of said second annular-form catalyst bed.

In a preferred embodiment, the above-described process is furthercharacterized in that the reaction chamber contains three annular-form,movable catalyst beds and (l) a heat-exehange fluid medium is introducedat a locus between the upper two of said catalyst beds, and (2) theresulting mixture of said fluid medium and the converted reactant streamfrom the next lower annular-form catalyst bed flows upwardly into asecond reactant conduit and laterally, in radial flow, through anannular-form third catalyst bed.

Other objects and embodiments will become evident from the following,more detailed description of our inventive concept, and the reactionsystem and process encompassed thereby.

SUMMARY OF INVENTION As hereinabove set forth, our invention isparticularly directed toward the multiple-stage contact and conversionof a fluid reactant stream in countercurrent flow with respect tocatalyst particles which are movable 1 through thc various stages by wayof gravity-flow.

heretofore given rise to a host of difficulties and attendant problems.These primarily stem from the fact that Countercurrent processing of areactant stream has the linear velocity of reactant or effluent vaporsincreases as they pass upwardly through the catalyst zone. As the linearvelocity increases, fluidization of a packed catalyst bed can occur tothe extent of destroying the optimum catalyst/reactant contact, and thusinduce catalyst breakage as a result of constant contact with internalequipment. In many processes, especially those which are significantlyexothermic, or endothermic, these difficulties are compounded by virtueof the necessity to-utilize intermediate heat-exchange fluids. Typicalof such processes are hydrocracking, especially for liquefiedpetroleumgas (LPG) production, steam reforming to produce substitutenatural gas (SNG) and ethylbenzene dehydrogenation to produce styrene,etc.

The above-mentioned processes, in addition to others, appear, to have acommon characteristic with respect to deactivation of the catalystparticles. This appears not'to be dependent upon either upflow, ordotrmflow contact of the catalyst with the reactant stream. In eithersituation, that segment of the catalyst lyst particles movable throughsaid stages via gravity-, k

flow, which process comprises the steps of: (a) intro-- ducing a firstportion of said reactant stream into a re-- action chamber, containingat least two vertically-disposed reaction zones, at a locus intermediatesaid re action zones; (b) passing said first portiondownwardly throughthe lower of said reaction zones, and flowing said portion laterally, inradial flow, through a first an? nular-form catalyst bed, in which thecatalyst particles are movable via gravity-flow, into a center reactantconduit; (c) introducing a second portion of said reactant stream intothe lower extremity of said center reactant conduit, within said lowerreaction zone; (d) introducing the resulting mixture. of said secondreactant stream portion and the reaction product of said first reactantstream portion into a center reactant conduit within the uppermost ofsaid reaction zones; (e) passing said mixture upwardly through saidupper reaction zone and flowing said mixture'laterally, in radial flow,through a second annulanform catalyst bed, in which the catalystparticles are movable via gravity-flow, into an outer annular-form voidvolume; and, (f) withdrawwhich "sees" the reactant stream first, willdeactivate first and at a significantly more rapid rate than theremaining portion of catalyst. As the zone of deactivated catalystproceeds through the entire catalyst bed, less becomes-availableforeffecting the desired reactions. Ultimately, of course, the entirecatalyst bed becomes deactivatedand the unit must beshut down forregeneration-or catalyst replacement. When utilizing a reac- J tiosystem in which the catalyst particles are movable,

via gravity-flowfirorn reaction stage to reaction stage, ultimatelybeing withdrawn from thesystem, in combination with countercurrent flowof the reactant stream, it is, possible to remove that catalyst which isdeactivated first, while simultaneously introducing fresh catalyst intothe uppermost stage. The withdrawn catalyst can either be transported toon-site regeneration facilities, or discarded for metals recovery. Thelatter is dependent principallyupon the cause of deactivation, and

whether techniques exist to regenerate the catalyst employed. Forexample, hydrocracking for LPG production generally utilizes a catalystof a Group VIII and/or Group Vl B metal combined with a refractoryinorganic oxide carrier material e.g. aluminasilica. deactivation ofthis catalyst generally stems from colte deposition, and regenerationthereof is readily possible. On the other hand, a steam reformingcatalyst i.e. nickel on silica/alumina with modifiers such as magnesiumoxide and/or copper-chromium complexes deactivates as a result of thecrystallite growth of the active metal, and is not readily subject toregeneration. in either situation, the utilization of ourinvention'prolongs the continuous on-stream time afforded betweenshut-downs either for catalyst regeneration, or the replacement thereof.

An additional advantage resides in a significant decrease in therequired catalyst inventory within the reaction chambers, especiallywith respect to catalyst which is not regenerable and must be replaced.Situations of this nature are perhaps best exemplified by considering amultiple-stage steam reforming process for SNG production.-Briefly, thisprocessis generally effected in two or more stages of gasification, withsplit feed, followed by one or more stagesof shift methanation toincrease the methane concentration. Considering only the gasificationstages, a typical two-stage unit designed to process about 30,000BbL/day ofa naphtha feed, requires about 382,000. pounds of catalyst(total in both stages) to function for about 1% years prior to ashut-down for catalyst replacement. The catalyst inventory in a unit ofthis capacity can be decreased by as much as -60 percent through the useof the present inventive concept, without the need for a shut-downexcept for the normal, periodic turn-arounds for maintenance purposes.

The multiple-stage reaction system herein described utilizedtubular-form components which may take any suitable shapes such astriangular, square, oblong, diamond, etc. Many design, fabrication andtechnical considerations dictate the advantages of using componentswhich are substantially circular in cross-section. While these will beevidentto those possessing the requisite'skill in catalytic processing,mention of the most important consideration-is warranted; that is,uniformity [of-catalystflowthroughout,the system, while countercurrently;flowing the reactant stream laterally and radially therethrough'. r

The basic component of the reaction system is a vertically-disposedreactionchamber containing at least two s'eparate, individua l reactionzones. in a preferred embodiment, the chamber contains three reactionzones as hereinafter described in conjunction with'the lower portion ofwhich fresh reactant stream, or re actant stream effluent froma lowerreaction zone is introduced. Alth ough the utilization of inner andouter catalyst-retaining screen members is preferred in formingtheannular-form, catalyst-holding sections,'the annular-form void volumeand the center reactant conduit,

these same essential elements can be formed through the utilization ofperforated cylinders. The primary consideration is thatftheopeningseither in the screen members, or in the perforated cylindrical members,be sized to prevent the migration of catalyst particles'intoaccompanying. drawings. These reactionf-.-zonesare the outerannular-form void volume, or into the center reactant conduit.

The reaction zones are spaced apart through the use of lower and upperimperforate transverse partitions. I n this regard, the followingdiscussion will be directed toward a reaction chamber having threeindividual reaction zones as illustrated in the accompanying drawings.With respect to the lowermost of the three reaction zones, the lower,imperforate transverse partition extends to, and is connected with theinterior wall of the reaction chamber, and to both the inner and outercatalyst-retaining screens; however, this lower imperforate transversepartition terminates at the inner catalyst-retaining screen such thatthe center reactant conduit is in open communication, at its lowerextremity, with a fluid reactant stream inlet conduit. The upperimperforate transverse partition, within the lowermost reaction zone, isconnected to both the inner and outer catalyst-retaining screen members,but terminates at the outer screen in order that the annular-form voidvolume between the outer screen and interior wall of the chamber is inopen communication with another fluid reactant stream inlet conduit.This upper imperforate transverse partition also terminates at the innercatalyst-retaining screen so that the center reactant conduit of thelowermost reaction zone is in open communication, or contiguous, withthe center reactant conduit of the next uppermost reaction zone. Thelower, imperforate transverse partition, disposed within the middlereaction zone, is similar to that disposed within the lowermost reactionzone; that is, it terminates at the inner catalyst-retaining screen, isattached to the outer catalyst-retaining screen and terminates at theinterior wall of the chamber. That portion of the innercatalyst-retaining screen which extends from the first upper,imperforate transverse partition to the second lower, imperforatetransverse partition is also imperforate.

In this manner, a first portion of the reactant stream is introducedinto the reaction chamber at a locus intermediate the middie andlowennost reaction zones. The locus is situated such that it isintermediate the second lower, imperforate transverse partition and thefirst upper, imperforate transverse partition. As the reactant stream'enters the reaction chamber, it is caused to flow downwardly throughthe lower annular-fonn void volume and laterally, in radial flow,through the annularform catalyst bed, disposed between the inner andouter catalyst-retaining screens, into the center reactant conduit. Asecond portion of the reactant stream is introduced into the lowermostextremity of the center reactant conduit, to be admixed therein with'the reactant product effluent from the lowermost reaction zone,themixture continuing upwardly into the middle reaction zone.-

The upper. imperforate transverse partition within the second, or middlereaction zone, is connected to both the inner and outercatalyst-retaining screens, but terminates at the outer screen. in thismanner, the reactant stream flowing upwardly through the center reactantconduit flows laterally, in radial fashion, in an inward-to-outwarddirection into the annular-form void volume. The lower, imperforatetransverse partition within the uppermost reaction zone is identical tothe lower, imperforate transverse partition disposed within thelowermost reaction zone. That is, it is connected to the interior wallof the chamber and both the inner and outer catalyst-retaining screens,but terminates at the inner screen such that the reactant streameffluent from the middle reaction zone is caused to flow upwardlythrough the center reactant conduit and laterally, in radial flow,through the uppermost annularform catalyst bed into the annular-formvoid volume. The upper, imperforate transverse partition within theuppermost reaction zone is virtually identical with that disposed withinthe middle reaction zone. In a preferred embodiment, a heat-exchangefluid medium is introduced at a locus intermediate the second upper,imperforatc transverse partition and the third lower, imperforatetransverse partition.

In a preferred method of operation, the heatexchange fluid inlet conduitdischarges upwardly into the center reactant conduit. The precisecharacter of the heat-exchange fluid is primarily dependent upon theprocess being effected, as well as whether the principal character ofthe reactions is exothermic, or endothermic. In the situation involvingthe hydrocracking of a normally liquid feedstock for LPG product, beinga highly exothermic reaction, the heat-exchange fluid may be hydrogen, ahydrocarbon stream such as unconverted feedstock which is beingrecycled, a portion of the desired product effluent, etc. Similarly, thesteam reforming of hydrocarbons to produce a methane-rich, substitutenatural gas, is a highly exothermic -reaction. Experience dictates thatthe heatexchange fluid effects a decrease in the temperature of thereaction stream effluent from the lower reaction zone; therefore, theheat-exchange fluid may consist of a portion of fresh feed charge stockinadmixture with steam, a portion of the fresh feed charge stock itself,or a portion of the methane-rich product effluent. An example of anendothermic reaction system is the dehydrogenation of ethylbenzene toproduce styrene. This entails the introduction .of high temperaturesteam as the heat-exchange fluid medium in order to reheat the;

reactant stream for processing in the succeeding upper reaction zone.

For the sole purpose of illustration, and not with the intent of undulylimiting the present invention beyond the scope and spirit of theappended claims, it willbe presumed that the various tubular-formcomponents are substantially circular in cross-section and further thatthe reaction system is being utilized in a steam reforming process forthe production of methane'rich SNG.

Steam reforming is generally effected with a steam to carbon ratio inthe range of about 1.1 to about 6.0, and preferably from about 1.3 toabout 4.0. The mixture is passed into a steam reforming reactionzone.(generally prepared or naturally-occurring. One particularlysuitable steam reforming catalyst is that described in US. Pat. No.3,429,680 (Cl. 48-214). which catalyst utilizes a carrier material ofkieselguhr and a catalytically active nickel component promoted by acopperchromium, or copper-chromium-manganese complex, and which may, ormay not be further promoted by the addition of an alkaline-earth metaloxide.

The reaction zone product effluent, principally comprising methane,carbon monoxide, carbon dioxide, hydrogen and steam is cooled to atemperature in the range of about 400F. to about 800F., preferably withan upper limit of about 650F. The cooled effluent is then introducedinto one or more shift methanation zones wherein the hydrogen and carbonmonoxide are converted into additional methane. Following the removal ofwater and carbon dioxide, the resulting SNG has a heating value of fromabout 950 to about lOOO BTU per cubic foot. It is to this type ofhydrocarbon processing that the present invention is particularlyapplicable; however. it is understood that there is no intent to solimit the scope of the appended claims.

DESCRIPTION OF DRAWINGS Briefly, FIG. 1 illustrates a stacked" reactionchambet 1, having three annular-form catalytic reaction zones 8", "C",and "D". As hereinafter described in greater detail, the upper portionof the reaction chamber constitutes a catalyst-treating zone A. FIG. 2is an enlarged, sectioned elevation showing the lower portion ofreaction zone 8", the center reaction zone C" and the upper portion ofreaction zone D". Catamultiple-stage) at a temperature such thatthefmaximum catalyst bed temperature is in the range of about 800 F. toabout I l00F., and preferably 'from about 825F. to about IQOOF. Steamreforming reactions are effected under an imposed pressure in therangeof about 250 psig. to about l500 psig., and preferably from about 400psig. to about 1000 psig.

A wide variety of steam reforming catalytic composites are well known,and have been thoroughly described in the appropriate literature. Ingeneral, these catalysts utilize metallic components selected from GroupVl-B and the iron-group of the Periodic Table. Also disclosed are thebenefits to be accrued through the utilization of catalytic promotersselected from alkali and alkaline-earth metals. These catalyticcomponents are generally combined with a suitable refractory inorganicoxide carrier material, either synthetically,

lyst particles and catalyst transfer conduits have been eliminated fromthe illustration in FIG. 2 as being nonessential to an understanding ofthe arrangement of the various components of the entire reaction system.

Further description of the reaction system encompassed by the presentinventive concept will be made in conjunction with a commercially-scaledunit designed to process approximately 33,000 barrels per day of anaphtha'boiling range charge stock having a gravity of about 68.8 APland an average molecular weight of l03.4. Analyses indicate that thenaphtha charge stock consists of about 88.2% by volume of paraff'ms,8.2% naphthenes and about 3.5% aromatics, and has the approximatecomponent analysis indicated in the following Table I:

Charge Stock Analysis Component Molt/Hour Total 3,199.6!

Equivalent to 32.l9l BblJday This particular process involves twogasification reaction zones, employing split feed; that is,approximately one-half of the charge stock is introduced into the firstgasification zone, the reactant stream effluent from which is admixedwith the second half of the charge stock prior to the introductionthereof into the second reaction zone. Furthermore, the unit utilizes amethanation reaction zone in order to reduce the concentration ofhydrogen and carbon monoxide in the product effluent, while increasingthe heating value of the ultimately desired product.

Specific reference now to FIG. 1, reaction chamber 1 is illustrated asconsisting of a catalyst-treating section A", an upper methanationreaction zone "B", an intermediate gasification reaction zone "C" and alower gasification reaction zone D". The catalytic composite, utilizedin both the gasification reaction zones as well as in the methanationreaction zone, comprises, on a weight percent basis, 8.0 silica, 45.0nickel, 14.0 magnesium, l.56 copper, l.l7 chromium and 0.14 manganese,the remainder being oxygen. This particular catalytic composite does notreadily lend itself to an oxidative regeneration technique in view ofthe fact that carbon deposition does not appear to be the primary causeof catalyst deactivation. Furthermore, in the process of steamreforming, utilizing the above-described, nickelcontaining catalyst, itis essential that the hot reactant stream does not contact cold"catalyst particles. Should such contact take place, water will condenseon the catalyst particles, thereby effecting a reaction between thenickel and carbon oxides to form nickel carbonyl. This, in turn,decomposes at elevated temperatures with the result that the.crystallite size of the nickel component increases and catalyst activityis severely, detrimentally affected. Therefore, catalysttreating sectionA" will function primarily as a heatexchange zone to raise thetemperature of the catalyst particles prior to the contact thereof inmethanation reaction zone "B".

Upper catalyst-treating section "A" contains a catalyst-holding zone 4formed by cylindrical member 5 and having a nominal cross-sectional arealess than that of the treating section, thereby providing annular space6 between the exterior of the catalyst-holding zone and the interior ofthe catalyst-treating section. Depending upon the particular treatmentaccorded to the catalyst within the catalyst-holding zone, for example,oxidation, reduction, sulfiding, heating, etc., cylindrical member 5will either be imperforate, or perforated to permit the reactanteffluent vapors to pass through the catalyst particles therein. in thepresent situation, as hereinbefore stated, the'catalyst particles mustbe heated to avoid the detrimental formation of nickel carbonyl.Therefore, cylindrical member 5 will be substantially imperforate, andcatalyst-treating section A will serve to accomplishindirectheat-exchange. Catalyst-holding zone 4, confined within cylindricalmember 5, is further defined by an upper imperforate plate 7 whichextends to the interior wall of the catalyst-holding section, andimperforate plate 8 which ter- 10 rninates at cylindrical member 5 toprovide an outer annular-form void volume 6 through which reactanteffluent vapors pass.

Fresh catalyst particles, or in many instances regenerated catalystparticles, are introduced into the uppermost portion of reaction chamber1 by way of catalystinlet port 2. These catalyst particles areintroduced thereby into catalyst-holding zone 4, wherein the temperaturethereof is increased by way of indirect-heatexchange with the reactanteffluent vapors in annularform void volume 6. Although the dimensions ofcatalyst-treating section "A" are dependent upon a wide variety offactors, including the treatment to be accorded the catalyst particles,a primary consideration is the average rate of catalyst withdrawal fromthe reaction chamber. In the present illustration, the average catalystwithdrawal rate approximates 20 pounds per hour, and thecatalyst-holding zone is designed to provide a residence time ofapproximately 2 hours.

The thus-treated catalyst particles are withdrawn from catalyst-holdingzone 4 by way of a principal catalysttransfer conduit 9. This mainconduit feeds into a plurality of secondary catalyst-transfer conduit 10generally numbering from about 6 to about 16, and uniforinly spacedthroughout the cross-sectional area of the upper portion of theannular-form catalyst bed in reaction zone 8''.

Similarly, catalyst particles are withdrawn, by way of gravity-flow,from catalyst bed 15 by way of a plurality of catalyst-transfer conduits24, again numbering from about 6 to about 16 and uniformly spacedthroughout the cross-sectional area of the catalyst bed. These catalystparticles are introduced into annular-form catalyst bed 20 disposed inreaction zone C". Catalyst-transfer conduits 25 are utilized to withdrawcatalyst particles from catalyst bed 20, and introduce the same intoannular-form catalyst bed 28 disposed in the lowermost reaction zone D".Deactivated catalyst particles are withdrawn, by way of a plurality ofcatalyst-withdrawal conduits 30, from the lowermost portion of reactionzone D". In many processes, as hereinbefore set forth, the main cause ofcatalyst deactivationis the deposition of coke and other carbonaceousmaterials. Therefore, the deactivated catalyst particles withdrawn byway of catalyst-withdrawal conduits 30 may be transported to anon-stream catalyst-regeneration facility which also functions with agravity-flowing catalyst bed. In the present illustration, since thecatalyst particles are not readily susceptible to oxidativeregeneration, they will be transported to a suitable metal-recoverysystem.

Approximately one-half of the fresh naphtha charge stock, hereinbeforedescribed, (1,585,98 moles per hour) is admixed with steam in the amountof 23,169.16 moles per hour. This mixture constitutes the fresh feed" toreaction zone "D" by way of inlet port 26. The temperature of the feedto reaction zone "D is about 900F., the hydrogen/naphtha mole ration isabout 0.3, the steam/carbon ratio is about 2.0 and the pressure is about600 psig.

Reaction zone "D" has disposed therein coaxiallydisposed, inner andouter tubular-form, catalyst-retaining screens 19 and 27, respectively.Both the inner and outer retaining screens are perforated substantiallyalong the entire length, and form therebetween an annular-form catalystbed 28. The nominal diameters of the catalyst-retaining screens are suchthat outer retaining screen 27 forms an annular-fonn void volume 34withthe interior wall of reaction zone "D", and

inner screen 19 provides a centrally located reactant conduit 22.Reaction zone D is defined, at its lowermost extremity, by asubstantially imperforate transverse partition 29. The use of the term"substantially impcrforate" is intended to connote that the transversepartition is provided with appropriate openings which permit catalystparticles to be withdrawn by way of catalyst-withdrawal conduits 30.Transverse partition 29 is connected to the interior wall of reactionzone "D", to inner catalyst-retaining screen 19 and to outercatalyst-retaining screen 27. However. the transverse partitionterminates at inner retaining screen 19 in order to provide anunrestricted passageway into center reactant conduit 22. Catalyst bed 28is also defined by an upper imperforate transverse partition 23connected to both the inner and outer catalyst-retaining screens 19 and27. As indicated in FIG. 1, transverse partition 23 terminates at boththe inner and outer catalystretaining screens. lt should be noted thatthe portion of inner catalyst-retaining screen 19 extending from upperimperforate transverse partition 23 to lower imperforate transversepartition 21, is imperforate. Therefore, the portion of the fresh feedcharge stock being introduced via port 26 initially flows downwardlythrough annular-form void volume 34, laterally and radially throughcatalyst bed 28 into center reactant conduit 22 and upwards intoreaction zone "C".

The second portion of the charge stock is introduced into the lowermostportion of reaction zone "D" by way of conduit 31, and is admixed withthe reactant product effluent in center reactant conduit 22. Componentanalyses of the charge stock entering conduit 26 and the reactionproduct effluent from reaction zone D" are given in the following Tablell:

Values in Moll/Hour The component analyses presented in Table I1 areexclusive of the fresh feed charge stock and inclusive of 653.43moles/hour of steam being introduced by way of inlet conduit 31. Theoutward to inward flow in reaction zone "D" has the effect of causingthe fresh feed charge stock to "see" a greater quantity of catalyst in ashorter period of time than would be the situation if the reactantstream flow were reversed. An additional advantage resides in the factthat catalyst bed 28 functions as a trash catcher, and is that catalystwhich is withdrawn from the reaction chamber.

Reaction zone C" is defined by a lower imperforate transverse partition21 which is connected to both the inner and outer catalyst-retainingscreens, 18 and 19, and to the interior wall of the reaction chamber. Anupper imperforate transverse partition 17 is connected only to the innerand outer catalyst retaining screens, and terminates at the outer screen18. Center reactant conduit 22 is continuous through both reaction zone"D" and reaction zone C" and terminates at upper transverse partition17. Therefore. the material in that portion of center reactant conduit22 flows laterally and radially through catalyst bed 20 into outer voidvolume 33. Component analyses of the total feed to reaction zone "C" andthe effluent therefrom are presented in the following Table III:

Values in Mala/Hour In order to decrease the concentration of hydrogenin the product effluent from reaction zone C", the temperature isdecreased to a level of about 550F. by introducing a sufficient portionof the ultimate SNG product by way of inlet port 35. At the lowertemperature, the hydrogen is caused to react with carbon dioxide andcarbon monoxide to produce additional methane and water. The mixtureflows into reaction zone "B" in center reactant conduit 14 and laterallyand radially through catalyst bed 15 defined by inner retaining screen13 and outer retaining screen 12. The product effluent from the shiftmethanation zone flows through outer void volume 32 intocatalyst-treating section "A".

Reaction zone "B" is defined by a lower imperforate transverse partition16 and an upper transverse partition 11. The lower transverse partitionis connected to i the interior wall of the reaction chamber and to bothcatalyst-retaining screens 12 and 13. However, it termi nates at innercatalyst-retaining screen 13. Upper transverse partition 11 is connectedto both the inner and outer catalyst-retaining screens and terminates atouter retaining screen 12 in order to provide uninhibited flow in outervoid volume 32.

The product effluent from reaction zone 8" utilized to heat the catalystparticles in catalyst-treating zone A". The product effluent from theshift methanation reaction zone is withdrawn by way of port 3. Acomponent analysis thereof is presented in the following Table IV:

TABLE IV Shift Methanation Effluent Analysis Component Mols/Hour Steam12692.33 Carbon Monoxide 0.56 Carbon Dioxide 5059.61 Hydrogen 168.13Methane 17751.92

13 technique employs a catalytic reaction system utilizing vanadiumpentoxide as the catalyst.

P10. 2 is a sectioned view ofa portion of the reaction chamber, andillustrates several preferred embodiments with respect to the internalconfiguration of the various reaction zone elements. It should be notedthat catalyst-retaining screen 19 is imperforate along that portion 36which extends from upper transverse partition 23 to lower transversepartition 21. Thus, the feed stock being introduced via inlet conduit 26is caused to How downwardly into the outer annular void volume, throughretaining screens 27 and 19, and into the center reactant conduit 22.Conversely, reaction zone "C" is defined by transverse partitions 21 and17 to effect inward to outward radial flow.

The cross-sectional area of that portion of center reactant conduit 22within reaction zone "C" is greater than that portion within reactionzone "D". Likewise, the cross-sectional area of center reactant conduit14 is greater than that of conduit 22 within reaction zone Thisparticular embodiment is preferred when consideration is given to thecombined velocity head. the pressure drop across the annular-formcatalyst beds, the critical path velocity and avoidance of channelingand fluidization of the catalyst. The heatexchange medium conduit 35preferably discharges upwardly into center reactant conduit 14 in orderto enhance the mixing thereof with the vaporous effluent from reactionzone C".

The methane-rich. substitute natural gas, following water and carbondioxide removal has a heating value of about 985 BTU per cubic foot.Catalyst inventory is reduced about 30.0%, and the system functionscontinuously for a period of about 2% years without being shut downexcept for routine maintenance purposes.

We claim as our invention:

1. A process for effecting the multiple-stage. countercurrent contactand conversion of a hydrocarbon reactant stream with hydrocarbonconversion catalyst particles movable through said stages viagravity-flow, which process comprises the steps of:

a. introducing a first portion of said reactant stream into a reactionchamber, containing at least two 14 vertically-disposed reaction zones.at a locus intermediate said reaction zones;

b. passing said first portion downwardly through the lower of saidreaction zones and flowing said portion laterally, in radial flow,through a first annularform catalyst bed. in which the catalystparticles are movable via gravity-flow. into a center reactant conduit;

c. introducing a second portion of said reactant stream into the lowerextremity of said center reactant conduit. within said lower reactionzone;

d. introducing the resulting mixture of said second reactant streamportion and the reaction product of said first reactant stream portioninto a center reactant conduit within the upper of said reaction zones;

e. passing said mixture upwardly through said upper reaction zone andflowing said mixture laterally. in radial flow. through a secondannular-form catalyst bed. in which the catalyst particles are movablevia gravity-flow. into an outer annular-form void volume; and,

f. withdrawing the resulting converted reactant stream from an upperportion of said second annulanform catalyst bed.

2. The process of claim 1 further characterized in that said reactionchamber contains three annularform. movable catalyst beds and (i) aheat-exchange fluid medium is introduced at a locus between the uppertwo of said catalyst beds, and (ii) the resulting mixture of said fluidmedium and the converted reactant stream from the next lowerannular-form catalyst bed flows upwardly into a center reactant conduitand laterally. in radial flow, through an annular-form third catalystbed.

3. The process of claim 1 further characterized in that said reactantstream is a mixture of steam and a naphtha boiling range hydrocarbonfraction.

4. The process of claim 2 further characterized in that saidheat-exchange fluid medium comprises methane.

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1. A PROCESS FOR EFFECTING THE MULTIPLE-STAGE, COUNTERCURRENT CONTACTAND CONVERSION OF A HYDROCARBON REACTANT STREAM WITH HYDROCARBONCONVERSION CATALYST PARTICLES MOVABLE THROUGH SAID STAGES VIAGRAVITY-FLOW, WHICH PROCESS COMPRISES THE STEPS OF A. INTRODUCING AFIRST PORTION OF SAID REACANT STREAM INTO A REACTION CHAMBER, CONTAININGAT LEAST TOW VERTICALLY-DISPOSED REACTION ZONES, AT A LOCUS INTERMEDIATESAID REACTION ZONES, B. PASSING SAID FIRST PORTION DOWNWARDLY THROUGHTHE LOWER OF SAID REACTION ZONES AND FLOWING SAID PORTION LATERALLY, INRADIAL FLOW, THROUGH A FIRST ANNULAR-FORM CATALYST BED, IN WHICH THECATALYST PARTICLES ARE MOVABLE VIA GRAVITYFLOW, INTO A CENTER REACTANTCONDUIT, C. INTRODUCING A SECOND PORTION OF SAID REACTANT STREAM INTOTHE LOWER EXTREMITY OF SAID CENTER REACANT CONDUIT, WITHIN SAID LOWERREACTION ZONE, D. INTRODUCING THE RESULTING MIXTURE OF SAID SECONDREACTANT STREAM PORTION AND THE REACTION PRODUCT OF SAID FIRST REACTANTSTREAM PORTION INTO A CENTER REACTANT CONDUIT WITHIN THE UPPER OF SAIDREACTION ZONES, E. PASSING SAID MIXTURE UPWARDLY THROUGH SAID UPPERREACTION ZONE AND FLOWING SAID MIXTURE LATERALLY, IN RADIAL FLOW,THROUGH A SECOND ANNULAR-FORM CATALYST BED, IN WHICH THE CATALYSTPARTICLES ARE MOVABLE VIA GRAVITY-FLOW, INTO AN OUTER ANNULAR-FORM VOIDVOLUME, AND, F. WITHDRAWING THE RESULTING CONVERTED REACTANT STREAM FROMAN UPPER PORTION OF SAID SECOND ANNULAR-FORM CATALYST BED.
 2. Theprocess of claim 1 further characterized in that said reaction chambercontains three annular-form, movable catalyst beds and (i) aheat-exchange fluid medium is introduced at a locus between the uppertwo of said catalyst beds, and (ii) the resulting mixture of said fluidmedium and the converted reactant stream from the next lowerannular-form catalyst bed flows upwardly into a center reactant conduitand laterally, in radial flow, through an annular-form third catalystbed.
 3. The process of claim 1 further characterized in that saidreactant stream is a mixture of steam and a naphtha boiling rangehydrocarbon fraction.
 4. The process of claim 2 further characterized inthat said heat-exchange fluid medium comprises methane.